Solid Glass Snail (Phenacolimax crassus)  

Glass snails are so-called ‘semi-slugs’, that means, they still bear a more or less reduced and transparent shell, into which they cannot any longer move their body, at least not completely. 

Several species are occurring in all over Europe with the most inhabiting the southern part of the continent.  

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The Solid Glass Snail was described in 1986, apparently basen on (sub)fossil shells which had been found on the island of Porto Santo in the Madeiran Archipelago.

The species is considered extinct. [1]

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References:  

[1] Robert A. D. Cameron; Laurence M. Cook; Glenn A. Goodfriend; Mary B. Seddon: Fossil land snail faunas of Porto Santo, Madeiran Archipelago: Change and stasis in Pleistocene to recent times. Malacologia 49(1): 25-59. 2006  

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edited: 16.06.2020